May 22 (GMM) Felipe Massa says his former Ferrari teammate Fernando Alonso made a clear "mistake" in leaving the Italian team.

Actually, Alonso insists he has no regrets about joining McLaren-Honda, as beating dominant Mercedes requires a new and innovative long-term project.

And the Spaniard has also said that his Ferrari successor Sebastian Vettel only won in Malaysia due to "circumstances", and that while the Maranello team might be better in 2015, it is still a long way from Mercedes.

Asked if he agrees with Alonso's reasoning, Massa said in Monaco: "Of course not.

"I think Alonso had to invent some reasons to justify a change that has certainly been more negative than positive," he told Brazil's Globo Esporte.

"Ferrari really has improved. I think it is difficult sometimes to admit when you've made a mistake," added Massa, who was Alonso's Ferrari teammate until the end of 2013.

And the Brazilian, who now drives for Williams, said the car is not the only change Ferrari has undergone in the last months.

"Ferrari changed everything!" said Massa. "The president, the team boss -- it's a different team."

Asked if the current regime might have seen him even retain his own seat at Ferrari, he admitted: "Maybe yes."

But Massa says he is so happy at Williams now that he is willing to stay for years. Ferrari, on the other hand, reportedly has its eye on Valtteri Bottas, who is Massa's current teammate.

Massa said: "It's something he can do in the future, but I don't think so for next year, because Williams has a contract option on him.

"But for the future, Ferrari is more competitive; it has shown potential to win and fight again for the championship. If he (Bottas) has a good proposal to go to Ferrari, why not?" he added.